Bench scale drum agglomerator and power means

ABSTRACT

A process and product of waste recovery at phosphorus furnaces is disclosed wherein small sized discrete particles of carbonaceous material or beneficiated phosphate ore are mixed with a mineral acid, an alkaline fluid and water, and the reacted mixture is tumbled in a horizontal cylinder at a temperature below that at which the carbonaceous material oxidizes to form agglomerates which are then indurated to discrete particulate size as desired for a charge component; the agglomerates are fed to a phosphorus smelting furnace together with other materials needed to make elemental phosphorus, furnace gases are cooled with recirculating water, a side stream of the water is taken off, treated, and used as feedstock in fluid fertilizers. Apparatus is disclosed for agglomerating coke and phosphate and, further, for measuring the abrasion and shatter resistance of agglomerates.

This application is a divisional application of my copending applicationSer. No. 223,122, filed Jan. 7, 1981 for ENERGY CONSERVATION ANDPOLLUTION ABATEMENT AT PHOSPHORUS FURNACES.

BACKGROUND OF THE INVENTION

1. Field of the Invention

My invention relates in general to energy conservation and wasterecovery at phosphorus furnaces, and it deals more particularly with aprocess and apparatus for waste recovery at phosphorus furnaces by lowenergy agglomeration thereof in a matched particulate component whichmay be used as a recharging component for such a furnace and for otherpurposes.

Elemental phosphorus is produced by smelting a mixture of mineralphosphate, coke, and silica rock in a submerged arc electric furnace.The mineral phosphate is usually agglomerated at high temperatures byprocesses similar to those employed in the metallurgical industry.Development of the phosphorus furnace process is described in a TVApublication ("Production of Elemental Phosphorus by the Electric-furnaceMethod," R. B. Burt and J. C. Barber, Chemical Engineering Report No. 3,1952, National Fertilizer Development Center, Muscle Shoals, Ala.35660). Development of agglomeration processes for phosphorus furnacefeed materials is given in another TVA publication ("Agglomeration ofPhosphate for Furnace Use," E. L Stout, Chemical Engineering Report No.4, National Fertilizer Development Center, Muscle Shoals, Ala. 35660).

It is noted that much particulate matter is emitted during hightemperature agglomeration of the phosphate. About 12 percent of thefluorine combined in the phosphate ore is evolved, although thispercentage will vary with the temperature. Much energy is expended inair pollution abatement, and water waste problems are created. Largequantities of fuel are consumed.

No fluorine is emitted with low temperature agglomeration of the mineralphosphates, and particulate emission is small. The energy requirement isreduced from the range of 2.5×10⁶ to 4×10⁶ million Btu per ton ofagglomerates to about 800,000 Btu.

Metallurgical coke is generally purchased for use as a reducing carbonin phosphorus furnaces. However, the coke fines (minus 10-mesh material)adversely affects furnace operation. About fifteen percent of thepurchased coke is fines. When the fines are removed, a solid wasteproblem is created unless some use can be found for this material.

I have discovered that mineral phosphates can be agglomerated at lowtemperature by a novel application of surface tension forces. Coke finesmay be agglomerated at low temperature by similar application of surfacetension forces to prepare properly sized material for use as a reducingcarbon in the phosphorus furnace according to the present invention.Also, the agglomeration processes may be applied to other carbonaceousmaterials, such as calcined anthracite, and thereby relieve the currentshortage of metallurgical coke.

My invention deals with the recovery of small sized coke material andcondenser bleed-off water at phosphorus furnaces. The small sized cokeis agglomerated by a new process, as described herein, and this willpermit the coke to be used in phosphorus furnaces as a reducing carbon.Condenser bleed-off water, after treatment, can be used as a feedstockin making fluid fertilizers. Sludge acid separates from merchant-gradewet-process phosphoric acid, and this waste material can be used as abinder in the new agglomeration process of this invention.

Likewise, flotation tailing is obtained when phosphate ores arebeneficiated. This new agglomerating process will permit this waste tobe combined with phosphate concentrates and agglomerated to make aself-fluxing furnace charge material. The improved agglomeration processmakes it possible to use phosphorus furnace charge materials withmatched average sizes and size distributions. As a result, segregationin the furnace is essentially eliminated and furnace pressurefluctuations reduced. The overall result is less electric energy usedfor smelting and less loss of elemental phosphorus from inleakage ofair.

2. Discussion of Prior Art

After a competent search of the state of the art, no existing processand product of waste recovery at phosphorus furnaces was disclosedembodying the principles of the present invention directed to suchpurposes, and no bench scale apparatus of the type used herein for suchagglomeration was revealed. The prior art discloses the following U.S.patents:

U.S. Pat. No. 2,040,081, Mar. 12, 1936, Harry A. Curtis. A process isdisclosed in this patent for the agglomeration of finely groundphosphate in a pug mill. This invention relates to the process ofagglomerating fine phosphate rock from an original ore.

U.S. Pat. No. 2,741,545, Apr. 10, 1956, F. T. Nielsson. This is aforerunner of all of the ammoniation-granulation patents in themanufacture of fertilizer.

U.S. Pat. No. 3,012,874, Dec. 12, 1961, A. B. Phillips, et al. In thispatent calcium metaphosphate is granulated with hot water.

U.S. Pat. No. 3,034,883, May 15, 1962, T. P. Hignett, et al. This is aprocess for the agglomeration of a fertilizer mixture wheresuperphosphate is produced in place in the binder.

U.S. Pat. No. 3,113,858, Dec. 10, 1963, A. V. Slack, et al. This is apatent which deals with the production of suspension fertilizers.

U.S. Pat. No. 3,177,062, Apr. 6, 1965, T. P. Hignett, et al. This is aprocess for granulating ground phosphate whereby elemental sulfur is thebinder.

U.S. Pat. No. 3,202,744, Aug. 24, 1965, J. C. Barber, et al. In thispatent, a phosphorus sludge is used as a binder to briquet phosphorusfurnace feed.

U.S. Pat. No. 3,335,094, Aug. 8, 1967, W. J. Darby. This is a processfor preparing a briquetted mixture of phosphate, silica and coke havinga high electrical resistance.

U.S. Pat. No. 3,464,809, Sept. 2, 1969, G. C. Hicks. This is a processfor making granular ammonium sulfate in the ammoniator-granulator.

U.S. Pat. No. 3,813,233, May 28, 1974, L. A. Kendrick, Jr. This is aprocess for making a high-analysis suspension fertilizer frommerchant-grade wet-process phosphoric acid.

SUMMARY AND OBJECTS OF THE INVENTION

A summary of the beneficial objects and features of my inventionnecessitate the consideration of the production of elemental phosphorusby the normal means of smelting a mixture of phosphate, coke and silicain an electric furnace. This has previously been referred to in a paperprepared by the inventor for the National Fertilizer Development Center,at Muscle Shoals, Ala. One ton of phosphorus normally requires 9.5 tonsof phosphate rock, 1.5 tons of coke, and 1.7 tons of silica rock. Thismixture is smelted by heat from submerged electric arcs to reducecombined phosphorus to the elemental form. Other materials formed in thephosphorus furnace are slag, consisting of calcium silicate and calciumaluminate; ferrophosphorus, and carbon monoxide gas. The gas leaving thefurnace is a mixture of phosphorus vapor, carbon monoxide, carbondioxide, methane, and hydrogen, but the principal constituents arecarbon monoxide and phosphorus vapor. The gas is cooled to condense theelemental phosphorus. Noncondensable constituents in the furnace gas areused as a fuel, or are flared.

The slag and ferrophosphorus are tapped from the furnace and may bedisposed of as by-products of phosphorus production.

Lump or agglomerated materials are generally required for use inphosphorus furnaces, although sizing of the phosphate feed is not asimportant for small furnaces as it is for large ones. Phosphate oresseldom occur in nature in the size range suitable for use in phosphorusfurnaces, and phosphate is agglomerated at the larger furnaces(powerloads of 25 megawatts or higher).

Phosphates are agglomerated by processes similar to those employed inthe metallurgical industry. In nodulizing, small size ores are heated tothe point of incipient fusion in a rotary kiln. Sufficient meltingoccurs to form a cohesive mixture of solid and liquid phases and themixture is tumbled to form agglomerates. Large amounts of energy areconsumed in this operation (3.5 to 4.0 million Btu per ton offurnaceable material). It is difficult to control the amount of liquidphase formed in the kiln, and the size of the agglomerated productvaries from balls as large as four feet in diameter to unagglomeratedfines. The large balls are crushed, small sized material is removed byscreening, and materials fed to the furnace will have a size range ofminus two inch to plus six mesh. The average size of the nodulizedphosphate is about 0.8 inch.

Phosphates may be agglomerated by pelletizing, briquetting, orcompacting. The agglomerates have low strength when they are formed butthey are indurated by calcination. The phosphates are calcined attemperatures below fusion and energy requirements for agglomeration areless than for nodulizing (2.5 to 3.0 million Btu per ton of furnaceableproduct.) Low grade phosphates generally contain clay and they are moreamenable to agglomeration than high grade phosphates. Clay serves as abinder in compacting and briquetting. In nodulizing, the clay fractionmelts at a lower temperature than does other materials in the ore.Unfortunately, clay has an adverse effect on phosphorus furnaceoperation, and low grade ores consume more energy during smelting thando high grade ores.

Silica rock is frequently available in lump form and no agglomeration isneeded. The silica rock is put into the phosphorus furnace to provide areactant (SiO₂) to combine with calcium oxide and form calcium silicate.Calcium oxide also combines with alumina in the phosphate to formcalcium aluminate. An SiO₂ :CaO weight ratio in the range of 0.85 to0.95 is adequate. Sometimes low grade phosphates may contain enough SiO₂and no silica rock is added. When lump silica rock is used, its sizeseldom matches the size of agglomerated phosphate. This leads tosegregation in the furnace.

The coke supplies carbon to combine with the oxygen and form carbonmonoxide, thereby reducing combined phosphorus to the element.Metallurgical coke is commonly used as the reducing carbon, but thecarbon may come from other sources such as petroleum coke, reformedcoke, anthracite coal, low-volatile bituminous coal, or charcoal.

Metallurgical coke consists of particles ranging from 100 mesh to3/4-inch in size. Materials smaller than 10 mesh are generally removedby screening. The minus 10 mesh coke fines are fed to the furnace at acontrolled rate, or the fines may be discarded as a solid waste. Cokefines are ineffective as a reducing agent; furthermore, phosphorusfurnace operation is improved by eliminating fines from the furnacecharge. Heretofore, technology has not been available to permit theeffective use of coke fines in the phosphorus furnace.

When the three furnace charge components--phosphate, silica, andcoke--have about the same size and size distribution, phosphorus furnaceoperation is markedly improved. A furnace power chart illustrates thedecrease in fluctuations of the powerload in changing from the regularcharge to a charge with matched particle sizes. The power chart withunmatched particle sizes showed great fluctuations when phosphate wasagglomerated by nodulizing. In such an operation, minus 10-mesh fineswere screened out of the coke, but these fines were fed back to thefurnace at a controlled rate to avoid accumulation of solid waste. Theaverage size of the nodules fed was about 0.8 inch and the average sizeof coke was 0.3 to 0.4 inch. The phosphate contained 23.5 to 24.5percent P₂ O₅ and it contained enough SiO₂ to provide a 0.85 SiO₂ :CaOratio in the charge. No silica rock was fed.

Minimal fluctuations showed on a power chart with matched sizes ofphosphate and coke. The phosphate contained enough SiO₂ and no silicarock was fed. The phosphate was briquetted and then calcined in a rotarykiln at a temperature of about 2200° F. to indurate the briquets.Average size of the phosphate fed to the furnace was 1.0 inch. Speciallarge size coke was purchased for the test and the coke was prepared togive an average size of about 1.0 inch. The coke and calcined briquetsfed to the furnace had about the same size distribution and there waslittle tendency for the materials to segregate.

The powerload on the furnace was set at 9400 kW but with the regularcharge the average powerload was 8100 kW, or 13.8 percent lower than theset load. When matched sizes of coke and phosphate were fed, the averagepowerload was 9300 kW, or 1.3 percent lower than the set load. Thesedata show that the capacity of a phosphorus furnace can be increasedabout 12 percent by changing from unmatched to matched charge sizes.

Similarly, when we examine a pressure chart for a furnace, it shows thedecrease in furnace pressure fluctuations that occur when unmatchedsizes of nodules and coke are replaced by matched sizes of thesematerials. In such a test run, using briquets for the matched sizecharge, the time on the graph was noted when matched size materialsfirst entered the furnace. This graph proved that pressure variationsdecreased markedly with the matched sizes of charge component.

The electrical energy consumption was about ten percent lower withmatched charge than it was with the regular charge of nodules and coke.However, the test run of two days was not long enough to obtain accuratedata, and it was impractical to obtain enough material to make a longertest.

Major benefits realized from use of closely matched charge material overunmatched material are summarized below:

1. Powerload fluctuations are decreased, and this permits the capacityof a furnace to be increased without expenditure for additionalproduction facilities. Fixed costs are thereby reduced.

2. Furnace pressure fluctuations are decreased and this decreases lossesof phosphorus caused by air being drawn into the furnace gas stream. Airoxidizes elemental phosphorus to P₂ O₅. When furnace pressurefluctuations are decreased, leakage of furnace gases into the workroomenvironment is lessened. Obnoxious and poisonous gases (P₂ O₅, CO, andfluorides) escape through openings in the furnace roof, feed chutes, andofftake ducts when the pressure increases.

3. The electrical energy consumed in smelting phosphate is reduced whenmatched charges are used.

The benefits from using matched sizes of furnace charge components havebeen known for about twelve years. Heretofore, agglomerating processesto make matched sizes of the furnace charge materials were unknown.

Gases leaving the phosphorus furnace consist mainly of carbon monoxideand phosphorus vapor. By volume, ten percent of the gas is phosphorusvapor. The gases are cooled to condense the phosphorus as a liquid.Water is brought into contact with phosphorus during condensing andstorage of the element and sometimes water is used in treating impurephosphorus. As a result, water becomes contaminated with elementalphosphorus, phosphoric acid, and fluosilicic acid and insoluble matter.Although the water may be used repeatedly in phosphorus condensingoperations, accumulation of contaminants will necessitate that part ofthe recirculating water be drawn off and replaced with fresh water.

Effluents containing elemental phosphorus are a serious water pollutionproblem. Watercourses containing about 40 parts per billion may be toxicto marine animals. Technology is not currently available for removal ofelemental phosphorus in water to a level which will render the waterinnocuous to marine animals.

Accordingly, one of the objects of the present invention is to provide asmall scale (bench scale) apparatus suitable for experimentalagglomeration. In connection therewith, another object of the presentinvention is to provide a low cost, lightweight agglomerator of the typedescribed with speed control equipment capable of turning the drum atany speed below the critical speed. In connection therewith, a featureof the assembly must be that it shall assume a size small enough toplace inside of a laboratory hood but large enough to obtain meaningfuldata on the agglomeration of materials such as coke and phosphate.

Another object of the present invention is to prepare mixtures of cokefines and acidic material which, upon ammoniating and tumbling in arotating drum, will be agglomerated to form particles large enough touse in phosphorus furnaces. Agglomeration of the coke fines in thismanner will permit recovery of the fines as a useful reducing agent, andwill avoid a solid waste problem at phosphorus furnaces.

Another object of the invention is to prepare mixtures of small sizedphosphate and acidic materials which, upon ammoniation, will agglomerateinto particles suitable for charging into the phosphorus furnace.Agglomeration of the small sized phosphate will aid in preparing matchedsizes of a furnace charge.

Another object is to prepare an agglomerated mixture of phosphateconcentrate and flotation tailing. Flotation tailing is obtained whenphosphate ores are beneficiated. The new agglomerating process willpermit this waste to be combined with phosphate concentrate andagglomerated to make a self-fluxing furnace charge material. Thephosphate concentrate thus obtained is the high grade phosphaticmaterial obtained by beneficiating phosphate ores, as aforesaid. Thetailing, or waste material, consists mainly of quartz silica, but italso contains some phosphate. It is an objective to prepare anagglomerated mixture which will have an SiO₂ :CaO weight ratio in therange of 0.85 to 0.95. The agglomerate will be self-fluxing andessentially without clay as an impurity.

Another object of the invention is to provide low energy consumingagglomeration processes for both phosphate and coke. Matched sizes ofphosphate and coke will be prepared, and this will eliminate segregationof the charge materials during smelting.

Another object is to use condenser bleedoff water as a feedstock formaking suspension fertilizers. The condenser bleedoff water is clarifiedand centrifuged to reduce the elemental phosphorus to about 12 ppm--aconcentration low enough to permit the waste to be used in making13.5-38-0 suspension fertilizer. The condenser bleedoff water mustundergo much more extensive treatment to reduce the elemental phosphoruscontent enough to render the waste innocuous to marine animals.Nutrients (N and P₂ O₅) in the wastes are recovered and fluosilicic acidis beneficial as a crystal modifier.

A final object is to use sludge acid as a binder in preparingagglomerates. Sludge acid results from the post-precipitation ofimpurities in merchant-grade wet-process phosphoric acid.

Thus it can be seen that features of this invention involve processesfor the recovery of small sized coke material and condenser bleedoffwater at phosphorus furnaces. The small sized coke is agglomerated by anew process and this will permit the coke to be used in phosphorusfurnaces as a reducing carbon. Condenser bleedoff water can be used asfeedstock in making a fluid fertilizer. Sludge acid separates frommerchant-grade wet-process phosphoric acid, and this waste material canbe used as a binder in the new agglomerating process. Flotation tailing,which is obtained when phosphate ores are beneficiated, can by this newprocess be combined with phosphate concentrate and agglomerated to makea self-fluxing furnace charge material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the bench scale drum and power means.

FIG. 2 is a section view taken along lines 2--2 of FIG. 1.

FIG. 3 is an end view of the drum of FIGS. 1 and 2.

FIG. 4 is a diagrammatic illustration of a plant-scale agglomerator,mixer and dryer assembly.

DETAILED DESCRIPTION OF THE INVENTION

As we have previously stated in the objects occupying the summary ofthis invention, much prior research in this field shows that to havematched sizes of phosphate and coke as the charge in a phosphorusfurnace is highly beneficial and results in a more efficient operation.Experimental data show that the capacity of a phosphorus furnace can beincreased about 12 percent by changing from unmatched to matched chargesizes.

At the same time, this research showed that there was a marked decreasein furnace pressure fluctuations which occurred when unmatched sizes ofnodules and coke were replaced by matched sizes of these materials. Thishas, as stated, reduced electrical energy consumption by approximatelyten percent.

As shown in FIG. 1, I have provided a small scale (bench scale)apparatus suitable for experimental agglomerations which comprises anextended lengthwise cylinder or drum 1, provided with a feed end 2 and adischarge end 3. Referring to FIGS. 2 and 3, the end of the drum 2 isprovided with a circular feed opening 4, while the discharge end 3 ofthe drum has located inwardly therefrom in spaced relation a movableretaining ring 5.

The retaining ring 5 is provided with a circular opening 6 and there arewelded to the retaining ring three nuts 7 spaced at 120° intervalsaround the circumference of the ring. Each of the nuts 7 receive screws8 which are adapted to be tightened against the surface of the inside ofthe cylinder.

To the discharge end of the drum there is welded a circular overlappingflange 10 to which is in turn secured a strap 11 by means of bolts 27and nuts 28.

To the center of strap 11 there is welded a universal joint 13 whoseouter end forms a drill shaft 14.

It can be seen that the shaft 14 is received by the chuck 15 of amounted drill 16. The electric drill 16 is suitably fastened to a woodenblock 18 which is in turn bolted fast to a table 19. The table 19 isprovided with a suitable discharge opening 20 immediately below the drumand below which opening is placed a dish 21 to receive the dischargedmaterial.

The drum 1 is mounted to rest on four rollers or casters 22, whichcasters are suitably fastened to baseplate 23 attached to the table 19.The table 19 has suitable leg blocks 24 which support the table awayfrom the main surface of the work area.

At the power end of the table there is mounted thereon a Variac type ofsolenoid control through which the power cord 26 for the drill 16passes. In this manner it can be seen that the rotating speed of thedrum or cylinder can be regulated from the discharge end.

The strap 11 can be removed for servicing or removal of the retainingring 5.

At the feed end of the drum, there is welded an L-shaped flange 29 whichstrikes the arm of a counter 30 mounted on the table 19.

Due to the fact that the speed with which the drum or cylinder isrotated in its mounting may vary and may be extended for periods oftime, it is necessary that a source of cooling air be supplied for themotor of the electric drill in the embodiment of the invention shown.Therefore, we have indicated that a hose 31 for cooling air should bemounted over the motor by suitable means in order to direct a blast ofair on the motor for cooling.

An apparatus of the type illustrated in the embodiment shown in FIGS. 1,2 and 3 has been used quite successfully for preparing small quantitiesof agglomerated materials. In an apparatus which I have constructed ofthis type, the drum is a cylinder ten inches in diameter by eighteeninches long. It is fabricated from 16-gauge A.I.S.I. type 304 stainlesssteel. The critical speed of the rotating cylinder is the speed abovewhich solid material will be carried around on the inside surface of thedrum by centrifugal force. This speed is determined by R=76.5/√d, whered is the diameter of the cylinder in feet and R is the critical speed inrevolutions per minute. The critical speed of the apparatus shown inFIG. 1 is 84 rpm. The variable speed drive is a 1/4-inch industrialelectric drill. Full speed is 1760 rpm, but the speed can be reduced bycontrols on the electric drill. Close speed control is achieved byinserting a variable speed reducer in the motor circuit, such as aVariac speed control commonly used with laboratory equipment. Operationfor periods up to 30 minutes at speeds lower than 84 rpm will cause themotor to overheat and burn up unless supplemental cooling is applied. Toprovide the necessary cooling, part of the motor housing was removed andcompressed air from the laboratory supply was applied on the motorwinding at a rate of 18 liters per minute. The drum is turned by a1/4-inch shaft which fits in the chuck on the electric drill which alsopermits the drum to be readily and easily removed from the assembly. Theentire assembly, as seen, is mounted on a wooden block, as shown, andthe apparatus is light enough to permit it to be readily moved about thelaboratory; and it is small enough to be placed under most laboratoryhoods.

As will be obvious, the mixing in the laboratory experiments was donefor the most part in a batch fashion, in a suitable tub, bowl or othercontainer, as will be indicated by the examples which follow hereafter.

Of course, referring more particularly to FIG. 4, it can readily be seenthat any number of commercial type mixers, agglomerators and dryers forindurating the agglomerates can be employed. One is diagrammaticallyshown in FIG. 4, wherein a mixer of the cylindrical rotating type 34 ismounted in sequence with a cylindrical rotating agglomerator 36.

The mixture is fed into the feed end of the mixer 35 and discharged intothe agglomerator from the discharge end 37, where it is received by thefeed end 38 of the agglomerator and moved there through to the dischargeend 39.

The agglomerator 36 would be provided with a sparger 40. Theagglomerated material would be discharged into the chute 41 which entersthe dryer 42, which is in turn fed by the hot air entering through thetube 43 and discharged through the tube 44. Within the dryer theagglomerated material is discharged on a moving belt 46 where it isindurated by the heat and discharged at point 47 in the process.

The following examples are offered to illustrate properly the use of theapparatus which is the subject of my invention and the process employed,as well as the composition of matter which is produced as a newcomposition.

EXAMPLE I

Metallurgical coke was purchased for use as a reducing carbon to makeelemental phosphorus. The incoming coke was dried and screened on a10-mesh screen to remove fines before the reducing carbon was blendedwith phosphate and silica. The minus 10-mesh coke fines were accumulatedas a solid waste.

The pile of coke fines absorbed moisture from rainfall, and someextraneous material larger than 10-mesh in size accumulated in the pile.A sample from the fines pile was obtained; the moisture content wasdetermined to be 8.2 percent. Part of the sample was screened on a12-mesh U.S. Sieve (openings 1.68 mm) to obtain material foragglomeration experiments. The plus 12-mesh material was rejected.

A sample of merchant-grade wet-process phosphoric acid (52-54% P₂ O₅)was obtained from a railroad car. Wet, screened coke and phosphoric acidwere mixed by hand in a plastic container in proportions of 330 grams ofcoke (wet basis) and 64 grams of acid. Ninety grams of water were added.Thirty-six grams of reagent aqua ammonia (29% NH₃) were added. Thequantity of ammonia added was inadequate for the complete neutralizationof the phosphoric acid; the N:P₂ O₅ weight ratio of the product was0.26, assuming all the ammonia reacted. The temperature of the mixtureincreased to 70° C. when ammonia was added.

The mixture was fed to the agglomerator shown in FIG. 1 in six equalportions at a rate of about 74 grams per minute. The agglomerator drumrotated at a speed of 45 rpm, or approximately half its critical speed.The drum was horizontal during the experiment. The mixture dischargedfrom the drum as rounded agglomerates after a retention time estimatedto be 20 to 30 seconds. The freshly formed agglomerates were easilydeformed. They fell about 1 inch onto an improvised ramp and rolled downthe ramp into a container. A jet of compressed air was used to assistthe agglomerates in rolling down the ramp. The agglomerates were dried 3hours at 120° C. in a drying oven. The dried material contained 9.5percent P₂ O₅ and 1.9 percent N. Essentially all of the material wasformed into agglomerates larger than the openings in a No. 6 U.S. Sieve(3.36-mm openings), and the average diameter of the agglomerates wasestimated to be 3/8-inch (9.5 mm). The average crushing strength of a3/8-inch diameter agglomerate was 11 pounds.

EXAMPLE II p An experiment similar to that described in Example I wascarried out using sludge acid as the binder instead of merchant-gradewet-process phosphoric acid. A sample of sludge acid was obtained frommaterial that had settled out in a railroad car used to transport themerchant-grade acid. The sludge was formed by post-precipitation ofimpurities in the acid during transit. The usual P₂ O₅ content of thesludge acid is 38 percent. A mixture was prepared containing thefollowing constituents.

440 grams of wet coke fines (405 grams on a dry basis)

120 grams of sludge acid

99 grams of aqua ammonia (29% NH₃)

100 grams of water

The P₂ O₅ content of the dried agglomerates was estimated to be 9.0percent, and the nitrogen content was calculated to be 4.9 percent witha N:P₂ O₅ weight ratio of 0.52. Although some ammonia volatilizedwithout reacting, it is believed that the sludge acid was neutralized todiammonium phosphate. The crushing strength of 3/8-inch agglomerates was7 pounds.

EXAMPLE III

Florida pebble phosphate was crushed to provide some material smallerthan 6 mesh in size. Fifty-nine percent was minus 6 mesh, plus 12 meshand 42 percent minus 12 mesh. A 500-gram sample of the phosphate fineswas mixed with 50 grams of water in a plastic container. The dampmixture was placed in the laboratory agglomerator shown in FIG. 1.

The agglomerator was operated batchwise during this experiment byinstalling a plate over the discharge end. The drum had a slope of 3°;the drum sloped toward the discharge end. The drum was rotated at aspeed of 60 rpm.

Merchant-grade wet-process phosphoric acid was injected into thetumbling material through openings in a stainless steel sparger tube.The sparger was placed at the 5 o'clock position as viewed from the feedend; the drum rotated counter-clockwise. The sparger was about 1 inchfrom the wall of the drum. One hundred grams of the acid was spargedinto the bed of material over a 9-minute period beginning at the startof rotation.

Fifty-five grams of anhydrous ammonia was sparged into the drum throughopenings in another stainless steel tube. The ammonia added was adequateto make diammonium phosphate, but no allowance was made for unreactedammonia. The ammonia sparger was about 1 inch from the cylinder wall,and it was located at the 4 o'clock position as viewed from the feedend. The ammonia was added over a 15-minute period beginning at thestart of rotation. Rotation of the drum was continued for 5 moreminutes, making the total time of rotation 20 minutes. A metal spatulawas used to divert material spilled from the sparger area toward thefeed end of the drum.

The batch of agglomerates was removed from the drum and dried 4 hours ina laboratory oven at 120° C. The average size of the agglomerates wasapproximately 1/4-inch. Eighty-nine percent was plus 6 mesh. The averagecrushing strength of 1/4-inch agglomerates was 9 pounds.

EXAMPLE IV

An agglomerating experiment was carried out using the same equipment andprocedure as that described in Example III. The formulation was asfollows.

500 grams of phosphate fines (minus 6 mesh)

50 grams of water

142 grams of sludge acid

55 grams of anhydrous ammonia

The screen analyses of the indurated agglomerates showed that 80 percentof the material was larger than 6 mesh and 20 percent was smaller thanthis mesh size. The average size of the agglomerates was about 1/4-inch.The crushing strength of 1/4-inch agglomerates was 8 pounds.

EXAMPLE V

This example illustrates the manner in which waste tailing fromphosphate ore beneficiation would be agglomerated and used as phosphorusfurnace charge. This example is based on background information onphosphate ore processing and beneficiation. The phosphate agglomerationprocesses given in Examples III and IV are applied in preparing anagglomerated self-fluxing phosphate mixture suitable for use inphosphorus furnaces.

Heretofore, clay present in phosphate ores has been utilized as a binderin preparing agglomerated phosphates for furnace feed. Clay is thebinder in making green briquets and compacted flakes, and theseagglomerates are more readily prepared when the phosphate contains arelatively large amount of clay. In nodulizing, clay in the phosphatereduces both the temperature of incipient fusion and the energy requiredfor agglomeration. Nodulizing kiln linings are rapidly deteriorated whenthe phosphate contains no clay as an impurity.

Clay has an adverse effect on phosphorus furnace operations.Agglomerated phosphate containing clay must be calcined to indurate andstabilize the crystal structure of the material in order for thematerial to be used successfully for the production of phosphorus. Withan agglomerated phosphate-clay mixture the material begins to fuse andconsolidate above the zone of reduction, and this prevents gasesgenerated by the reduction reactions from flowing uniformly through thefurnace charge. However, lump phosphates which contain no clay can beused successfully in phosphorus furnaces without calcination. Apublication entitled "Phosphorus Furnace Operations--How Are TheyAffected by Various Types of Phosphate Charges?" by J. C. Barber and E.C. Marks, Journal of Metals, December 1962, gives more detailedinformation on the effect of various types of phosphates on furnaceoperation.

In phosphate ore beneficiation, clay is separated from the ore inhydroseparators and cyclones. Clay is in the overflow and is discardedas waste slimes. In Florida the underflow generally undergoes flotationto separate the phosphate values from the quartz impurity. The quartzcomes out as flotation tailing--another solid waste from onebeneficiation. However, the tailing can be used in building roads anddikes, and in some cases the tailing has been used to dewater slimes.Phosphate concentrate is produced from beneficiation by the flotationprocess.

For the present example, phosphate concentrate is mixed with flotationtailing in porportions needed to provide a SiO₂ :CaO weight ratio of0.85. The mixture is self-fluxing; that is, the phosphate containsenough SiO₂ to combine with the CaO. Proportions are 73 percentphosphate concentrate and 27 percent flotation tailing. (The concentratecontained 30.5% P₂ O₅.) About 4.6 percent of the P₂ O₅ in the mixturecomes from waste tailing. Composition of the mixture is as follows.

P₂ O₅ : 23.4 percent

CaO: 35.1 percent

SiO₂ : 29.8 percent

Fe₂ O₃ : 1.0 percent

Al₂ O₃ : 1.2 percent

The mixture of phosphate concentrate and flotation tailing normallyconsists of particles smaller than 16-mesh--a size that is readilyagglomerated by the laboratory apparatus shown in FIG. 1. FIG. 4illustrates the arrangement of plant equipment to be used inagglomerating and indurating the mixture of concentrate and tailing. Thefollowing proportions of materials are put in the rotary mixer.

0.733 ton phosphate concentrate

0.267 ton flotation tailing

0.100 ton water

0.160 ton of sludge acid containing about 38% P₂ O₅

Water provides sufficient liquid phase for agglomeration and the sludgeacid is the binder. Operation is continuous and the materials flow fromthe mixer into the agglomerator. Anhydrous ammonia is sparged into theagglomerator at a rate of 0.060 ton per ton of phosphate feed. The greenagglomerates discharge onto a wire mesh belt which conveys the materialunder a drying hood. The agglomerates are heated to a temperature ofabout 250° F. by hot air. The indurated agglomerates are screened on a6-mesh screen and the fines are recycled to the mixer. About 10 percentof the indurated agglomerates is fines. The plus 6-mesh agglomerates,containing 24.7 percent P₂ O₅, are fed to the phosphorus furnace withsufficient coke needed for reduction. No silica rock is required.

EXAMPLE VI

A phosphorus plant produces elemental phosphorus at a rate of 109 tonsper day. Furnace gases are treated in an electrostatic precipitator toremove particulate matter, and the gases are then contacted with watersprays in a spray condenser consisting of an open cylindrical chamber.The mixture of water and liquid phosphorus flows from the condenser to asump; liquid phosphorus collects in the bottom of the sump and the wateroverflows into another sump. The water is recirculated to the spraycondenser by pumping.

The gas mixture leaving the spray condenser consists of noncondensablegases (CO, CO₂, CH₄, and N₂) and uncondensed phosphorus vapor. The gasesare exhausted by wet vacuum pumps (Nash Hytor pumps) using condenserwater as the fluid in the pumps. The gases are pumped to a surfacecondenser (tubular) for further cooling and condensation of elementalphosphorus. The condenser tubes are irrigated by spraying condenserwater inside the tubes. Liquid phosphorus recovered in the spraycondenser and surface condenser is pumped to storage tanks where it isstored under water to keep it from burning.

Water contacts elemental phosphorus at the following places:

1. Spray condenser

2. Exhauster pumps

3. Surface condenser

4. Storage tanks

The water is saturated with elemental phosphorus and phosphorusparticles become suspended in the water. Water contaminated in thismanner is commonly called "phossy" water.

In this example phossy water is generated at a rate of 1300 gallons perton of phosphorus produced, and the water contains 1700 ppm of elementalphosphorus. The quantity of elemental phosphorus is 1.0 ton per day.Phossy water is treated in a clarifier at a rate of 99 gallons perminute. A commercial flocculating agent is added to aid in theclarification process. Overflow is the clarified water, and its rate is97 gallons per minute. Underflow from the clarifier contains the settledsolids which are treated to recover phosphorus values. Composition ofthe overflow is as follows:

    ______________________________________                                                       Grams per liter                                                ______________________________________                                        Elemental phosphorus                                                                           120                                                          Fluorine         10                                                           P.sub.2 O.sub.5  17                                                           NH.sub.3         9                                                            ______________________________________                                    

The overflow is returned to the phosphorus condensing system. However,accumulations of dissolved salts make it necessary to bleed offclarified water at a rate of 6 gallons per minute and replace this waterwith fresh water. The fluoride content of the water is not permitted toexceed 10 grams per liter to assure that fluosilicate concentrations donot reach saturation.

Clarified water bled from the system is mixed with plant cooling waterto give a mixture containing about 23 ppm of elemental phosphorus. Themixture is further clarified by settling in a 14-acre pond. Pondoverflow contains an average of 0.3 to 0.4 ppm of elemental phosphorus,but sometimes the phosphorus content at the pond outlet will go up to1.0 to 2.0 ppm. The pond overflow discharges to a receiving stream.

Elemental phosphorus is very toxic to marine animals. Publishedinformation ["Toxicity of Yellow Phosphorus to Herring (Clupeaharengus), Atlantic Salmon (Salmo salar), Lobster (Homarus americanus),and Beach Flea (Gammarus oceanicus)" V. Zitko, D. E. Aiken, S. N. Tibbo,K. W. T. Besch, and J. M. Anderson, Journal of Fisheries Research BoardCanada, 27, No. 1, 21-29, 1970] has shown that elemental phosphoruscontents of water as low as 40 parts per billion will kill some speciesof marine animals. Consequently, the phossy water treating methoddescribed in this example is not adequate for water pollution abatement,but heretofore no better abatement technology was known.

EXAMPLE VII

This example shows how wastewater from a phosphorus plant can be used asfeedstock for making a suspension fertilizer and thereby avoid thedischarge of any water waste contaminated with elemental phosphorus.

Phosphorus is produced at a rate of 109 tons per day and phossy waterfrom the condensing system containing 1700 ppm of elemental phosphorusis treated in a clarifier at a rate of 99 gpm. Overflow from theclarifier contains 120 ppm of elemental phosphorus and the rate is 97gallons per minute. A stream of clarified water is bled off to controlthe concentration of dissolved fluosilicates. The bleedoff rate is 6gallons per minute. The bleedoff water is treated in a stacked diskcentrifuge at a rate of 29 gallons per minute. (The centrifuge isoperated about 20 percent of the time to treat bleedoff water.) Thecentrifuge overflow rate is 25 gallons per minute and the overflowcontains 12 ppm of elemental phosphorus.

An ortho suspension fertilizer (13.5-38-0) is produced at the same siteby three-step neutralization of merchant-grade wet-process phosphoricacid at a rate of 20 tons per hour. (The suspension fertilizer plantoperates about 35 percent of the time.) The N:P₂ O₅ weight ratio is0.33. Attapulgite clay is added to keep the diammonium phosphatecrystals in suspension. The quantity of materials needed to make one ton(2,000 pounds) of the suspension fertilizer is as follows:

Phosphoric acid: 1,407 pounds

Anhydrous ammonia: 328 pounds

Water: 350 pounds

Clay: 30 pounds

Water is evaporated in the first stage of neutralization which occurs atthe boiling point (230° F.). Also, water is evaporated in an evaporativecooler. Total loss of water by evaporation is 115 pounds per ton of13.5-38-0 suspension fertilizer. The 350 pounds of water added per tonof suspension fertilizer is to replace water lost by evaporation and toprovide dilution water for the process.

The centrifuge overflow is used as feedstock instead of water. Theelemental phosphorus content of the suspension fertilizer is less than 1ppm--a concentration that causes no phytotoxicity problem in fluidfertilizers. Furthermore, the elemental phosphorus is rapidly oxidizedwhen applied to the soil ("Detoxification of White Phosphorus in Soil"by Hinrich L. Bohn, Journal of Agricultural and Food Chemistry, Vol. 18,No. 6, 1970.) The centrifuge overflow supplies 0.7 percent of thenutrients in 13.5-38-0 suspension fertilizer and reduces the nutrientcost $1.00 per ton of fertilizer produced.

EXAMPLE VIII

Phossy water generated in a 109 ton per day phosphorus plant is treatedas described in Example VII. Centrifuge overflow water is obtained at arate of 25 gpm and the water contains 12 ppm of elemental phosphorus.

Ortho suspension fertilizer (11-39-0) is produced by a two-stepammoniation process. The N:P₂ O₅ weight ratio is in the range of 0.27 to0.33--the weight ratio resulting in the highest solubility of nutrients.From 0.1 to 0.5 percent fluosilicic acid is added as a crystal modifierto form small needlelike monoammonium phosphate crystals as described inU.S. Defensive Publication T986,001, Sept. 4, 1979.

Centrifuge overflow water is used as feedstock in place of waternormally used. The centrifuge overflow water supplies the fluosilicicacid needed to modify the size and shape of monoammonium phosphatecrystals, and no fluosilicic acid is added. The fluosilicic acid contentof the suspension fertilizer is 0.23 percent.

Thus it will be seen that I have provided an apparatus suitably adaptedto meet the object and features hereinbefore set forth. It will furtherbe seen that I have provided a method or process well adapted for abatch type laboratory embodiment but obviously applicable to continuousprocesses following the same steps to achieve the same ends.

From the foregoing it will be seen that the invention is well adapted toattain all of the ends and objects together with other advantages whichare obvious and which are inherent to the apparatus, the method orprocess, and that a new composition of matter has been invented.

While I have shown and described particular embodiments of my invention,modifications and variations thereof will occur to those skilled in theart. I wish it to be understood, therefore, that the appended claims areintended to cover such modifications and variations which are within thetrue scope and spirit of my invention.

Having thus described the invention, what is claimed is:
 1. Bench scaleapparatus for agglomerating discrete solid particles by joining the samewith a salt crystallized from a solution, comprising:a rotatably mountedhorizontal cylinder with a ratio of diameter length of 0.3 to 0.8;variable drive means for said cylinder including a single phase electricmotor; transfer means for said driving force including a sequentiallyconnected universal joint; means for control of the speed of cylinderrotation including a variable electric resistance in the motor circuit;said control means varying the speed of rotation in the range of 25 to75 percent of the critical speed, where such critical speed isdetermined by the formula R=76.5/√d where d is the diameter of thecylinder in feet and R is the critical speed in rpm to produceagglomerates by tumbling in said cylinder; removable end plates in saidcylinder having concentric openings 60 to 70 percent of the cylinderdiameter; air cooling means directed on said motor; a mounting baseplate for said assembly sized to fit into a laboratory hood.
 2. A benchscale apparatus for agglomeration and a shatter resistancedetermination, all as described in claim 1, wherein:said end plates aresolid surface without openings; ball bearings are loaded into saidcylinder with agglomerated material; such that a decrease in size ofsaid agglomerates after tumbling is taken as a measure of abrasion andshatter resistance.